Thermal dye diffusion or sublimation transfer systems have been developed to obtain prints from pictures that have been generated electronically, for example, from a color video camera or digital camera. Details of this process and apparatus for practicing it are contained in U.S. Pat. No. 4,621,271 to Brownstein.
Thermal transfer works by transmitting heat through a donor from the backside to a dye-donor layer on the opposite side. When the dyes in the dye-donor layer are heated sufficiently, they sublime or diffuse, transferring to an adjacent receiving layer of the receiver element.
All imaging dyes are unstable to light to a greater or lesser degree. Dyes are known to photolytically degrade via a number of paths which often involve dye triplet states, radicals and/or singlet oxygen. The light degradation is further known to occur to different degrees depending upon the color of the dyes, i.e.: yellow, magenta, cyan, or mixtures thereof. Multiple dye light stabilizing compounds may be required to significantly improve overall thermal transfer image stability. Each individual dye light stabilizing compound may provide a small improvement which adds to the overall stabilization by a chosen set of materials. Thus, for any given stabilizing compound any demonstrated improvement in light stability is highly desirable.
Combinations of dyes and stabilizing compounds can result in different light fastnesses. For example, even if enhanced light fastness of a magenta dye is achieved, that of a cyan dye may not be achieved, resulting in poor color balance of images. In a thermal transfer recording material having formed images, dyes forming yellow, magenta and cyan images exist in an identical layer, in which a dye exhibiting poorest light fastness is affected by the other dyes, resulting in a hue shift in color mixing in the neutral or gray images leading to apparently deteriorated images.
The stabilizing compound may be incorporated into the dye layer of a donor element, it may be incorporated into a separate donor element, it may be incorporated into a separate portion of a donor element with repeating areas of dyes, or it may be incorporated into the dye receiving element. Incorporation of individual stabilizing compounds has been described in the prior patent literature most notably: U.S. Pat. Nos. 4,705,522, 4,855,281, 5,288,691, 5,342,728, 5,618,773, 5,620,941, 5,627,129, and recently, U.S. Patent Application Publication 2005/0233902. The materials described in these publications include, for example, phenols, epoxy compounds, alkoxy aryl compounds, dialkoxy aryl compounds, trialkoxy aryl compounds, alkyl or cycloalkyl substituted alkoxy aryl compounds, sulfonamido substituted aryl compounds, and hindered amine light stabilizing compounds.
U.S. Pat. Publication No. 2005/0233902 discloses a thermal transfer recording material, comprising an ink sheet having an ink layer containing a dye and an image receiving sheet having a dye receiving layer, wherein the ink sheet or the image receiving sheet contains an antioxidant exhibiting an oxidation potential of not less then 1000 mV (vs. SCE). However, the publication does not mention the specific set of stabilizing compounds of the present invention.
U.S. Pat. No. 5,426,022 discloses a photographic recording material with at least one silver halide emulsion layer, that contains novel light stabilizers for the azomethine dyes produced during chromogenic development. JP2005092035A2 (Fuji) discloses a color fade preventing agent for use in silver halide color photographic paper to provide good image stability. JP62178962 (Konishiroku Photo Industry Co. Ltd.) discloses phenylenediamine derivative-type dye image stabilizers for use in silver halide color photographic materials to give dye images with improved lightfastness and few stains. However, these references fail to disclose the specific compounds containing alkoxy groups and a urea group for use in thermal dye transfer materials required to stabilize thermal dye transfer images.